The present invention, in some embodiments thereof, relates to touch detection with a capacitive based digitizer system and, more particularly, but not exclusively, to a method for multi-touch detection with a grid based capacitive digitizer sensor and/or touch screen.
Digitizer systems that include capacitive sensors are commonly used as input devices for a variety of Human Interface Devices (HIDs) and for a variety of different applications. A touch-screen is one type of digitizer system that is integrated with a Flat Panel Display (FPD). Touch-screens are often used for operating portable devices, such as laptop computers, tablet computers, MP3 players, smart phones and other devices. Touch screens offer a more intuitive and versatile manner for interacting with an electronic product as compared to other known input devices. Touch screens can be used for example to select virtual buttons displayed on the screen, to manipulate size and position of displayed objects, to enter data with a virtual keyboard, virtual number pad and/or by handwritten input, to open a document or application, to scroll within a window, to draw and/or to play games. Some touch screens support multi-touch operations where multiple simultaneous touches can be used to provide input. Multi-touch operations can be used to perform more advance operations with a touch screen.
Many touch screens use a grid based capacitive sensor and/or a mutual capacitive sensor for touch detection. Multi-touch is typically supported by sequentially triggering each row or column in the grid and while detecting the electrical effect of the triggering on the crossing rows or columns.
U.S. Pat. No. 7,843,439, entitled “Touch Detection for a Digitizer” assigned to N-Trig Ltd., the contents of which is incorporated herein by reference, describes a digitizing system including a transparent digitizer sensor overlaid on a flat panel display (FPD). The transparent digitizing sensor includes a matrix of vertical and horizontal conductive lines for sensing location of one or more of a stylus and/or a finger. Input to the digitizer sensor includes one or more of electromagnetic (EM) transmission from the stylus touching the sensing surface and capacitive coupling due to a conductive object such as a finger touching the screen. Location of a finger is detected by triggering one conductive line at a time along one axis of the grid and detecting output in response to each signal applied from a plurality of conductive lines along the other axis. Based on this method, the digitizing system is capable of detecting position of simultaneous occurrences of multiple styluses and/or multiple finger touches.
U.S. Pat. No. 7,902,840 entitled “Apparatus for object information detection and methods of using same”, assigned to N-trig, the contents of which are hereby incorporated by reference describes a method for detecting an object on a sensor sensitive to capacitive coupling. The method includes simultaneously transmitting signals on at least two electrodes of the sensor with non-mutually interfering (orthogonal) frequencies, and sampling output from at least one other electrode crossing the at least two electrodes. The sampled signal is responsive to capacitive coupling formed between each of the at least two electrodes and the at least one other crossing electrode. One or more objects positioned over the sensor can be detected from the sampled signals. It is described that the simultaneous transmitting can be used to speed up report rate.
U.S. Pat. No. 8,338,724 entitled “Methods and Systems for detecting a position-based attribute of an object using digital codes”, the contents of which are hereby incorporated by reference describes a code division multiplexing technique that can be applied with a position sensor such as a touchpad to improve noise immunity and/or to provide performance enhancements. It is described that code division multiplexing can be used to create two or more distinct modulation signals that are simultaneously applied to transmitter electrodes within the sensor, thereby increasing the effective power of the applied signals. The distinct modulation signals are described as digitally encoded signals that are orthogonal to each other. Corresponding output from receiver electrodes are demodulated to identify position of an object anywhere on the position sensor.